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Special Senses:
Hearing, Taste, Smell
Peripheral Nervous System
Chapter 8
The Senses
 General senses of touch (tactile)
 Temperature - thermoreceptors (heat)
 Pressure - mechanoreceptors (movement)
 Pain - mechanoreceptors
 Special senses
 Smell - chemoreceptors (chemicals)
 Taste - chemoreceptors
 Sight - photoreceptors (light)
 Hearing - mechanoreceptors
 Equilibrium - (balance) mechanoreceptors
The Ear: Hearing and Balance

Two functions: Hearing and Balance
 Hearing:
Sound vibrations
 Equilibrium: Gross movements
 Mechanoreceptors:
respond to physical forces
 Both respond to different stimuli and
activated separately
Anatomy of Ear
HEARING
ONLY
HEARING
&
BALANCE
Anatomy of Ear
Why do we need earwax???

Divided into 3 regions:
 External,
Middle,
Internal
Earwax
protects
delicate
lining of meatus
(auditory canal) and helps prevent
 External Ear
microorganisms from entering the ear
 Auricle
(pinna) and Auditory Canal
 Ceruminous Glands in canal secrete earwax
 Tympanic membrane - eardrum
Anatomy of Ear

Middle Ear
 Tympanic
Cavity – air filled, mucosa-
lined
 Eustachian Tube – connects to throat
 Auditory ossicles (tiny bones) –
hammer, anvil, stirrup
Pressure build up
Swallowing
yawning
“VALSALVA”
Eustacian tube
THROAT
Otitis media



http://www.petearclinic.com/images_video.htm

http://apps.uwhealth.org/health/hie/2/19596.htm
Middle ear inflammation
Common with sore
throat in children
Enlarge, inflamed
eardrum
Pus, fluid build up
requires incision and
tubes to relieve pressure
and drain
Anatomy of Ear

INNER EAR
 This is a cavity
 Bony labyrinth – bony
chamber divided into
3 regions
Cochlea
 Vestibule
 Semicircular Canals


Two fluids:
Endolymph
 Perilymph

Labyrinth:
an intricate, sometimes
confusing, arrangement or
pattern
Sound waves Hearing
> external acoustic meatus
eardrum >
ossicles >
oval window >
set fluid in motion >
vibrations stimulate
“hair
cells” >duct,
Within
Cochlear
membranous labyrinth is
cochlear nerve transmits Spiral
impulse
to midbrain
Organ
of Corti – >
receptors
auditory cortex ofhearing
temporal
lobe or “hair
cells”
Figure 8.15
How the ear works…
http://www.youtube.com/watch?v=dCyz8eAs1I
What is a cochlear implant?
https://www.youtube.com/watch?v=zeg4qTnYO
pw
Cochlear implants
https://www.youtube.com/watch?v=6FhgYcfZZ
Y8

Hearing Loss
The following factors contribute to age-related hearing loss:




Family history (tends to run in families)
Repeated exposure to loud noises
Smoking (smokers are more likely to have such hearing
loss than nonsmokers)
Certain medical conditions and medications also
contribute to age-related hearing loss. About half of all
people over age 75 have some amount of age-related
hearing loss.
Chemical Senses: Taste and Smell

Chemoreceptor – respond to chemicals in
solution
OLFACTORY = smell
 GUSTATORY = taste




Five types of receptors for taste
Olfactory receptors much more sensitive
Complement each other, respond to same
stimuli
 Smell not as good as animals; however, some people
are wine tasters, perfumers
 If you smell a particular odor all day, you won’t
recognize its presence, you become accustomed, ex.
garbage men
 During old age, people lose sense of smell- lots of
perfume
 Humans can distinguish 10,000 or so chemicals
 What we really smell is pain: ex. chili, ammonia,
menthol (cold)
 Specific chemicals cause specific patterns of neurons
to fire
How the nose works…

http://www.youtube.com/watch?v=dIDBGUPRUI
Olfactory
epithelium
Olfactory tract
Olfactory bulb
Nasal
conchae
(a)
Route of
inhaled air
Figure 15.21a
Olfactory Receptors: Smell

1000’s of olfactory receptors roof of nasal cavity

Sniffing intensifies sense of smell

Olfactory receptor cells have olfactory hairs –
long cilia – in mucus layer

Chemicals in mucus layer stimulate hairs ->
filaments -> nerve

Olfactory impressions long lasting – memories,
adaptive
Figure
8.17
Olfactory
tract
Mitral cell (output cell)
Glomeruli
Olfactory bulb
Cribriform plate of ethmoid bone
Filaments of olfactory nerve
Olfactory
gland
Lamina propria connective tissue
Axon
Basal cell
Olfactory receptor cell
Olfactory
epithelium
Supporting cell
Mucus
(b)
Dendrite
Olfactory cilia
Route of inhaled air
containing odor molecules
Figure 15.21a
Pathway of smell
Nostril >
nasal cavity >
olfactory receptors (sensory neurons)
in membrane (top of nasal cavity) >
through ethmoid (bone) >
olfactory neurons in olfactory bulb
> brain
Taste Buds and Taste



Most pleasurable sense
Approx. 10,000 taste
buds, most on tongue
Papillae – projections,
taste buds found on
sides


Circumvallate papillae –
sides of tongue
Fungiform papillae –
top, more numerous
Figure 8.18
How the tongue works…

https://www.youtube.com/watch?v=KuPKj7MHes
Taste Buds
Filiform
papilla
Fungiform
papilla
Circumvallate Papilla
Connective tissue
Tongue epithelium
Taste Buds
Gustatory cells –
Chewed food mixes with saliva
respond to chemicals
 solution slides down to sides of papillae
 Gustatory hairs –
 enters taste pore
microvilli,
protrude through taste
 stimulate gustatory hairs
pore
 stimulate gustatory receptor cells

 impulse travels by nerves to brain
Figure 8.18
Five Taste Sensations







SWEET – sugars, saccharine,
salts
SOUR -- acids
BITTER – alkaloids
SALTY – metal ions in
solution
UMAMI– glutamate, “beef
taste” and MSG
Only slight differences in
receptor location.
Most buds respond to 2+
stimuli
http://pactlab-dev.spcomm.uiuc.edu/classes/08SP/280blogs/first_weblog3/2008/02/digitizing-your-taste-buds.html
Taste

Homeostatic role
Tastes for salt or sugar – minerals or carbs
 Sour – Oranges, lemons – Vitamin C
 Umami – protein intake
 Bitter – most poisons and spoiled food bitter,
protective

Factors of Taste

Temperature, texture


Spicy food excites pain receptors in mouth
Taste and Smell Complementary

Eating when you have cold
Ghost chile pepper from India
Heat
Exceptionally hot
Scoville rating 330,000–1,000,000
liquid Oleoresin Capsicum
Loss of Taste & Smell

Beginning in 60’s ability to taste and smell
diminishes

Decrease in # of receptors

About 50% over 80 cannot smell

Sense of taste is poor
Loss of Taste & Smell

Various other factors also can contribute to loss of taste
and smell, however, including:

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Nasal and sinus problems, such as allergies, sinusitis or
nasal polyps
Certain medications, including beta blockers and
angiotensin-converting enzyme (ACE) inhibitors
Tooth decay or poor dental hygiene
Cigarette smoking
Head or facial injury
Alzheimer's disease
Parkinson's disease
Impact of LOSS

Quality of life, often leading to decreased
appetite and poor nutrition

Contributes to depression

Might tempt you to use excess salt or sugar on
your food to enhance the taste — which could
be a problem if you have high blood pressure
or diabetes
Homeostatic Imbalances
of the EAR & NOSE
Disorder
Otitis media (292)
Conduction
deafness (297)
Sensorineural
deafness (297)
Anosmias (300)
Cause
Effect
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